1. Field of the Invention
The present invention relates to a magnetic head assembly in a double-side recording type disc driving apparatus capable of reading and writing information at both sides of a disc-like magnetic recording medium.
2. Description of the Prior Art
As to a double-side recording type disc driving apparatus which performs reading and writing of information at both sides of a disc-like magnetic recording medium (hereinafter referred to simply as "disc"), there are three types according to which position a magnetic head supported by a gimbal spring is disposed. They are a lower fixed, upper movable type in which the gimbal spring is disposed on the carriage side; an upper fixed, lower movable type in which the gimbal spring is disposed on the hold case side; and an upper movable, lower movable type in which the gimbal spring is provided on both carriage and hold case sides.
As an example of the upper movable, lower movable type, there is the invention disclosed in Japanese Patent Publication No. 43826/1983, which invention has been effected with a view to improving the follow-up performance of a magnetic head to thereby prevent off-track. An outline thereof will now be explained with reference to FIGS. 9 and 10 which are a longitudinal sectional view of a conventional magnetic head supporting device and a bottom view of a fore end portion of a magnetic head supporting movable base as viewed from the disc side, respectively.
In those figures, the magnetic head supporting device is mainly composed of a fixed base 1, a movable base 2 attached to a seat 3 of the fixed base 1 rotatably only within a certain range by means of a spring, and magnetic heads 9 and 10 mounted on fore end portions of the fixed base 1 and movable base 2, respectively. More specifically, the magnetic head 9 is attached through a gimbal spring 7 to a window portion 5 formed in the fixed base 1 and the magnetic head 10 is attached through a gimbal spring 8 to a window portion 6 formed in the movable base 2 so that heads are opposed to each other through a disc 15. Support pins 11 and 12 are in abutment with the backs of the gimbal springs 7 and 8 so that the magnetic heads 9 and 10 cannot move back from predetermined positions. Further, a fore end portion of a pressure spring 13 is in abutment with an upper surface of the movable base 2 to compress the latter toward the fixed base 1. A lifting hook 14 is projecting from the fore end side of the movable base 2 whereby the base 2 can be moved toward and away from the fixed base 1. As shown in FIG. 10, the gimbal spring 8 which supports the upper magnetic head 10 is obtained by punching a single thin-walled spring material to form a square portion "a" at a central portion and a square frame "b" at a peripheral edge portion, the square portion "a" and the square frame "b" being interconnected through a pair of narrow portions "c". Tongue pieces "d" are projecting from the square frame "b" in directions perpendicular to the narrow portions "c", and through the tongue pieces "d" the gimbal spring is bonded and fixed to the movable base 2. The gimbal spring 7 which supports the lower magnetic head 9 is of the same construction as the gimbal spring 8.
In the conventional magnetic head supporting device (magnetic head assembly) having the gimbal springs 7 and 8 of the above structure, when the magnetic heads 9 and 10 come into sliding contact with the upper surface of the disc 15 which is rotating at high speed in the direction of arrow A, an undulating phenomenon of particularly the square frame "b" may be developed by a frictional force generated between the heads and the disc. The undulating phenomenon causes resonance in an audible range of frequency band and this resonance may cause a so-called head squeak which involves an audible sound. According to one example of the method of suppressing the head squeak, vibration insulators are disposed at fore ends of the support pins 11 and 12 and the gimbal springs 7 and 8 are supported through the vibration insulators to dampen the undulating phenomenon of the square frame "b" and suppress the resonance in the audible range. However, this method has not been so effective for the gimbal spring 8 on the side of the movable base 2. This is presumed to be for the following reason. Since the fixed base 1 is integral with the disc driving apparatus through a guide rod (not shown), an increased mass causes drop in resonance frequency of the gimbal spring 7 on the side of the fixed base 1, resulting in that the resonance is difficult to appear as an audible sound, while the movable base 2 is mounted on the side of the fixed base 1 through the spring 4, so a small mass allows the vibration of the gimbal spring 8 to be transferred also to the movable base 2, resulting in that the gimbal spring 8 and the movable base 2 may resonate in the audible range despite of interposition of the vibration insulator.
For excluding the resonance of the gimbal spring 8 on the side of the movable base 2, there has been proposed a construction in which a damper, also called a dynamic damper, is attached to the movable base 2 and the phase of the movable base 2 and that of the dynamic damper are shifted from each other by a predetermined amount to prevent resonation. However, this method has not been a preferable solution because excess mass is applied to the movable base 2 and it may affect the follow-up performance of the magnetic head